Distance determining system



Jan. 6, E942. G, GUANELLA DISTANCE DETERMINING SYSTEM Filed March 6, 1940 4 Sheets-Sheet l AMP/.wee

INVENTOR ATTORNEY jam. 6, 1942. G. GUANELLA DISTANCE DETERMINING SYSTEM Filed March 6, 1940 4 Sheets-Sheet 2 R]- ML/F/fe INVENTOR A ./L. M? @fm M 7 ..l @A G m Jan. 5, i942. G, GUANELLA DISTANCE DETERMINING SYSTEM 4 Sheets-Sheet 5 Filed March 6, 1940 HMA/H68 lNvENTo Gl/SAV GIM/EMA BY b/ i@ ATTORNEY Ba 6, w42- G. GuANl-:LLA 2,268,587

DI STANCE' DETERMINING SYSTEM ATTORNEY .Patented Jan. n, waz

UNH@

genesi FECE Gustav Guanella, Zurich, Switzerland, assignor to Radio Patents Corporation, a corporation of New York Application March 6, 1940, Serial No. 322,459 In Switzerland March 3l, 1939 17 Claims.

The present invention relates to a system for and method of distance determination based on the principle of causing a radiant energy signal to travel to and back from a remote point and determining the distance travelled by measuring the transmitting time elapsed between the transmission and reception of the signal,

More particularly the invention is concerned with distance measuring systems of the above character employing a frequency modulated oscillation transmitted or projected towards a distant point and means for beating the received oscillation with a signal or oscillation directly applied from the transmitter to the receiver and utiliz-ing the beat frequency as a magnitude for determining the distance travelled.

According to a known method for measuring the altitude of an aeroplane above ground, radio waves are transmitted from the plane towards the ground, the frequency of which increases and decreases linearly or uniformly with respect to time. In a system of this type the constant difference between the frequencies of the transmittcd and reflected oscillation is proportional to the transmitting time; that is, in turn to the altitude of the plane above ground. Thus, the altitude can be measured by determining the beat frequency between the transmitted and received oscillation. A system of this type is described in detail in the Proceedings of the Institute of Radio Engineers, 1938, page 848, et seq.

In altimeters of the aforementioned type serving` as navigation aids for aircraft and the like, undesirable beat frequencies caused by incident interfering signals or disturbances result in sub-` I stantial errors and impairment of the distance measurement. In particular, if the frequency of the beats to be determined is small compared with the interfering beat frequency, considerable errors may occur in the altitude or distance indication even with a low signal-to-noise ratio of the receiver.

Accordingly, an object of the present invention is the provision of means and a novel method enabling a distance determination substantially v without interference and measuring errors caused by disturbing oscillations and other objectionable signals incident upon the receiver.

With this general object in view the invention involves the transmission and reception-after reflection or retransmission from a distant point-of an oscillatory signal whose frequency is subjected to continuous and periodic variations according to a 10W frequency un being a nonuniform or non-linear function with respect to 55 time. At least one periodically varying contro magnitude is derived from the beat frequenc; resulting from the transmitted and reflected 0s cillations which bears a predetermined relatioi to the momentary beat frequency. A componen or harmonic of this control magnitude is selecte: by suitable frequency discriminating means ani measured to serve as a means for determining th` distance travelled by the signals to and from thi remote object. 4

The invention both as regards the underlyin; principle thereof and the details and means fo. carrying it into practice will become more appar ent from the following detailed description of sev eral practical embodiments thereof taken witl reference to the accompanying drawings form'in; part of this specification and wherein:

Figure l shows in block diagram form the gen eral outlay of a system according to the inven tion,

Figure 2 shows theoretical diagrams explana tory of the function and operation of the inven tion,

Figures 3 to 7 are schematic circuit diagram. illustrating various modications of a distano measuring system designed and operating in ac 'cordance with the invention,

Figures 8 and 9 illustrate in block diagran form further modications for practicing the in vention,

Figure l0 is a block diagram illustrating the in ventive system with transmitting and receiving stations spaced at a considerable distance,

Figure 11 illustrates in block diagram form ai arrangement according to the invention fo transmitting a signal to a remote point and re laying or retransmitting the signal back to th point of transmission for determining the dis tance of said point from the transmitter in ac cordance with the invention.

Referring more particularly to Figure 1 show ingthe general outlay of a distance determinin; system according to the invention, item T repre sents th'e radiant energy transmitter such as radio transmitter and R the receiver placed clos to each other, such as on an aeroplane or at an; other desired location. A portion e1 of the fre quency modulated oscillations eo generated by th transmitter T is directly applied to the receive R, whilst another portion e2 of the oscillations i transmitted or projected towards a distant poin or object X and returned to the receiver R by re transmission or reflection as indicated by th dashed line in the diagram. If the distance o the object X is equal to d and the velocity o pagation equal to c, the period to required for signal to travel to and from th'e remote point letermined as follows:

other words, the reflected signal e2 will arrive `;he receiver R with a ltime delay to compared h the directly transmitted signal e1. By meascg this time delay or transmission period, the `:ance d may be determined as is understood rn the above. The signals e1 and e2 are mixed or intermoduad in the receiver Rin such a manner that the quency w of the output signal e of the receiver l be equal to the beat frequency w3 between rnd e2. Due to the non-uniform periodic var- .on of the transmitting frequency, this beat quency also has a periodic character starting rn zero to a maximum and back to zero again, is understood. By applying the signal e to a quency control device or frequency demodu- )r K a control magnitude E is produced havan amplitude which bears a predetermined ition to the momentary beat frequency be- :en the signals e1 and e2. The amplitude of at st one component or harmonic u of this conl magnitude is measured by an indicating iniment I which may be directly calibrated in ts of distance d, while the effect of all the reining components and interfering signals is `pressed kby a frequency discriminating ar- .gement or a filter F. Thus, in contrast to the ive mentioned known method, th'e invention olves the use of a determined frequency comarein U represents the amplitude and o the .'ular frequency, the oscillation transmitted l directly applied to the receiver is representby the following mathematical expression:

Brein E1 represents the constant amplitude l Bo.v=W represents the frequency swing or iation from the main or carrier frequency that is, the maximum frequency variation of transmitted oscillations. The momentary guency w1 of this oscillation is then expressed `ollows:

he oscillation e2 reflected or retransmitted n the remote point X will arrive at the re- 'er with a delay to according to Equation 1; t is, e2 is represented by the following exssion:

. the momentary frequency of this reflected llation will be as follows:

uo=Uo. sin ct ei=E1 sin (wot-Bo cos vt) The two oscillations e1 and ez result in a beat in the receiver having the following frequency:

Since ufo in practice is always small compared with 1, Equation 7 may be written with sufficient approximation as follows:

This beat frequency fluctuates in the rhythm of the low frequency o between zero and a maximum value W.c.to, which is dependent upon the transmitting period to and may serve as a measure of the distance d. Since a negative sign of wa has no practical meaning, the special brackets: [cos of] indicate that the positive absolute values are to be used in the formula. In carrying out the method, the conditions should be chosen in such a manner that the average beat frequency for the travelling periods to be dealt with is large compared with the modulating frequency o.

By rectification of the frequency mixture (ei-l-ez) a medium frequency signal es is produced in a known manner whose frequency corresponds at all times to the beat frequency and which is expressed as follows:

ea=E3 cos (fwaot) :E3 cos (Win. sin of) (9) wa=W.c.to. [cos ct] `Such amedium frequency signal may also be obtained by mutually intermodulating the oscillations er and e2, it being well known that a difference frequency is obtained by such intermodulation.

According to the present invention, the frequency w3 of e3 is tested by the aid of means which are selective to the periodic frequency variations in the rhythm of the low frequency in such a manner as to substantially suppress the effect of disturbing signals. This control is effected by the aid of a periodically varying magnitude having an amplitude whose Yfrequency bears a predetermined relation to the frequency w3 and is subjected to the same periodic fluctua tions as the latter. By transmitting this magnitude through a suitable frequency discriminating filter or applying it to any other discriminating device, the effect of interfering signals is substantially' reduced or eliminated. From the magnitude thus filtered the average beat frequency and in turn the distance d is determined by a simple amplitude measurement.

There are Various Ways for producing a control magnitude and suppressing undesirable components of this magnitude and other interfering signals. Thus, for instance, es may be rectified to obtain a potential E3 varying according to the amplitude of e3. This amplitude is maintained constant independently of amplitude fluctuations of the transmitted and received oscillations e1 land e2 as caused by fading, etc., by utilizing E3 as a control potential for automatically maintaining the amplification of the receiver at a constant value, thereby substantially eliminating any amplitude uctuation of the output signal es. In order to produce a control potential E's proportional to the distance d, the potential e3 maintained at a constant amplitude in the manner as above described is transmitted through a network having a varying propagation factor mw) dependent on frequency, whereby the output of this network supplies an alternating potential e5 expressed as follows:

By rectification of this signal there is obtained a control potential:

If the amplitude E3 is maintained at a constant value and if p(w) is directly proportional to the frequency, the propagation factor due to Equation 8 and for A1 being a constant will be as follows:

mwa) :A1.w3 (12) resulting in the following control potential:

E E3.."} .`w3 :A5-17.1121501005 Ut] whose amplitude in case of B5 being a constant is proportional to the transmitting period to. By this selective segregation the disturbing components contained in the controlling magnitude B5 of various origins are substantially eliminated. By measurement of us by the aid of a suitably calibrated alternating current instrument it is possible to obtain a direct indication of the distances d in accordance with Expressions 1 and 14. Also, in case of a non-linear function of the propagation ratio mw) of the filter transmitting the oscillation e3. a direct indication of the distance is possible by a corresponding non-linear calibration of the indicating instrument.

In case of frequency modulation of the carrier frequency wn in accordance with a periodic but non-sinusoidal low frequency uo, the amplitudes of the individual components of the control potential will deviate from the values given in Equation 13 but by suitably choosing the shape of uo, E5 may be such as to contain only a single alternating current component in which case no further components are suppressed by the filter circuit.

A controlling magnitude which corresponds at all times to the momentary frequency of e3 may further be produced by regulating the amplitude E3 of e5 by the aid of an automatic gain control arrangement in such a manner that the rectified output potential E5 has a constant amplitude. If the propagation factor puo) is inversely proportional to the frequency; that is, if

wherein A5 is a constant if the amplitude E5 is of constant value. In this case a similar relationship exists for the potential E3 to that given in Equation 13 whereby this potential may serve as a control magnitude in a manner as described hereinabove.

Since an accurate amplitude control of E; or E5 in the manner described often involves great difficulties, it is advantageous according to a feature of the invention to determine the ratio q of the amplitudes of a5 and us which ratio, for reasons as will be obvious, depends solely upon the propagation ratio p(w) dependent on f; quency, while any simultaneous amplitude var tions of es and us will be without influence this ratio.

This ratio may, for instance, be determined the form of the quotient of the direct potenti U5 and E3 obtained from u5 and es by recti( tion and subsequent filtering. According to c embodiment, these direct potentials are appli to the relatively displaced coils of a crossed-cc single-pointer ratio meter which may be direc calibrated in values of the distance d. If p( is proportional to the frequency, the amplitt U5 of u5 according to Equation 14 is as follov Since B5 is proportional to the amplitude A5 a in turn to the amplitude E3 of e3, the ratio q determined as follows:

q E3 Caio wherein C5 is a constant which is independf of amplitude.

The comparison of u5 and ea or U5 and Es spectively, may also be effected by deriving frl es a potential es by means of a network havi an adjustable amplitude propagation ratio in( pendent of frequency and by equalizing the a plitude E8 of es with the amplitude U5 of by adjusting the propagation ratio by the aid a suitable adjusting member. The adjusting 1 sition of the network is representative of 1 amplitude ratio q (see Equation 18) and in t1. of the distance d which latter may be direc read from a suitable scale associated with 1 adjusting member.

A selective control of a determined componi of the control magnitude E5 such as accordi to Equation 13 is furthermore possible by for` ing a product of this magnitude and a harmo: segregated from the low frequency un employ to frequency modulate the transmitted oscil tions such as the second harmonic:

uzzUz cos 2vt (l This product uv has an average or mean valuf which is dependent only upon the component having a frequency 2v. By this selective s1 pression of the effect of all components of 1 control magnitude deviating from a predetl mined frequency; i. e. 2v in the example chos a special lter or selective means are dispen: with. The formation of the mean product nf. be effected in a known manner by intermoc lating the respective electrical magnitudes a by subsequent smoothing or by directly produci a combined mechanical torque by means oi watt meter type instrument.

Finally, the distance determination may effected by a pair of control magnitudes c pendent upon the frequency according to d ferent laws or relationships. Thus, a first alt nating potential e5 may be produced by trai mitting es through a first network having transmission ratio pmu) dependent upon f: quency, while a second alternating potential is produced likewise by transmitting es throu a second network having a different propagati ratio dependent upon frequency p2(w). Th both e5 and es are determined by relations z cording to Equation 10. By rectification of th pzh/U3) :A21/U32 EG=E3.2.LU32= 1/2AG.W2.'U2.02 1 -l-COS 2WD control potential contains a component 'LL6=B6.02. COS 211i ag an amplitude U6=Be.to2. The ratio ben us and the component us contained in E5 ."ding to Equation 14 is directly proportional le transmitting period to and in turn to the nce d according to the following expression:

Qt==0so same applies to the ratio between the poten- U5 and Us obtained by rectification of us ue, respectively. This quotient can be ;ured by the aid of any known ratio indicatlevice such as a crossed-coil ratio meter. In r to substantially eliminate all interfering ionents, us and us are passed through electrillters and/or the comparison of these potenis eifected by means of a frequency selecrnethod. The variations of p1(w) and p2 w lpendence upon frequency may deviate from examples given in Equations 12 and 2l in h case too the quotient q is related to the f period to according to a denite, though lost cases non-linear, law. the momentary frequency w3 of the beat frecy potential e3 is too high or too small for ucing a control potential in dependence upon iency, a new intermediate frequency poten- :4 may be produced by frequency multiplicaor sub-division having a frequency Iein n is an integer number or fraction with iteger denominator. From e4 there is derived east one control magnitude E5 dependent frequency serving for indicating the trans- .ng period or distance in the manner deed hereinabove. This transmitting period rding to Equation 8 is proportional to the frequency w3. Since in this case instead of 1ere is present an n times higher frequencyI nere is obtained in accordance with Equation n indication equal to n times the travelling d. This may be taken into consideration by ,ble calibration of the indicating instru-` a frequency multiplication or sub-division s is not practicable, the frequency of the tls e1 and ez to be compared may be stepped down to obtain new signals en and 612 havrequencies w11 and w12 as follows:

ectication or intermodulation of these siga new intermediate signal having a differfrequency wi is obtained in accordance with .tion 24.

.e oscillations utilized for the distance deter- .tion in accordance with the invention may `of the side bands being also variable,

be of any desired character in accordance with existing requirements such as electro-magnetic waves, in particular short or ultra short waves, acoustic or compressional oscillations whose frequency may be Within the superaudible or any other range as may be desired. In determining the distance of a reecting point lying in a definite direction, it is advisable to use directional transmitting and receiving devices. In determining the distances along electrical conductors, the oscillations may be impressed upon the conductors in the form of electric currents or potentials.

The oscillations of Varying frequency may furthermore be transmitted to the distant point in the form of a modulated carrier which latter may be an electro-magnetic or a mechanical wave. This carrier wave which originally has a constant frequency is decomposed into at least two side bands by the modulation in accordance with the variable frequency signals, the frequency At the receiver input there are produced by demodulation the oscillations retarded in proportion to the travelling distance and whose frequency varies periodically and continuously. It is advisable to employ amplitude modulation for this type of carrier transmission in which case the amplitude of the transmitted oscillations varies according to the momentary value of the frequency modulated oscillations. Such a transmission is advantageous if the transmitting medium is not suited for transmission of oscillations of varying frequency or if better results are obtained with a transmitter and receiver for high frequencies and a correspondingly reduced modulation band width.

Referring more particularly to Figure 3 of the drawings, there is shown a system suited, although not limitatively, for determining the altitude of an aeroplane above the ground X by means of ultra short electric waves. The transmitter T2 comprises a three-electrode vacuum tube l! arranged in so-called braking field connection to produce mico-ray electric waves of extremely short wave length in accordance with the Barkhausen method. For this purpose the grid is maintained at a high positive potential by means of a battery or the like connected to the grid in series with a choke coil I4, while the plate is maintained at zero or slightly negative potential relative to the cathode by the aid of a further battery in series with choke coil I3. As is well known, the frequency of an electron oscillator of this type is dependent to a substantial degree upon the operating potential, in particular the grid potential, whereby frequency modulation in the rhythm of a low frequency potential un is eifected in a simple manner by superimposing the potential uo by way of a transformer I2 upon the steady grid potential such as shown in the diagram. The high frequency oscillations are transmitted through a Lecher wire system to the directional radiating system T1 comprising in the example shown a dipole antenna located at the focus of a parabolic reflector. The oscillations e0 thus transmitted in the form of a narrow beam are reflected by the object X (ground) and will arrive at the directional receiver R1 in the form of oscillations e2 being retarded relative to the directly transmitted oscillations e1 from the transmitter to the receiver, the delay period depending upon the travelling time to and from the distant object. In the receiver R2 there are produced by combination of the oscillations e1 and e2 beats having a frequency w3 according to Equations 7 and 8'. The receiver Rz shown comprises a circuit similar to that of the transmitter T2 embodying a three-electrode tube l5 arranged in braking field connection with positive and negative potential sources connected to the grid and anode through choke coils i6 and l1, respectively. By suitable adjustment of the operating constants of such a circuit, the average anode potential varies in the rhythm of the beat frequency. This beat frequency potential is transmitted by way of transformer I8 to an amplifier V. `After amplification in the latter, the intermediate frequency potential .e3 is applied to anl amplitude limiting system L serving to suppress the effect of amplitude fluctuations caused by fading, etc., upon the distance indication. The limiting device in the example shown has the form of a three-electrode vacuum tube I9 to the grid of which the oscillations e3 are applied by way of a coupling inductance 2| and a resistance 20 in series with the grid circuit. Since a positive grid potential is lavoided by the grid current fiowing through the resistance 20 and as the anode current decreases rapidly when the grid becomes negative, there are developed across the anode resistance 22 a series of impulses at a frequency w3 of constant amplitude substantially independently of the amplitude of the input oscillations.

The measurement of the frequency w3 for determining the travelling period to may be effected by applying the output signal of the limiter L to a filter or network having a propagation ratio dependent upon frequency and subsequent amplitude measurement. In the example illustrated in Figure 3, there is provided a different converting system K not requiring any special filters and adapted to produce a potential E being proportional at all times to the momentary frequency w3. The function of the system K is as follows: the output impulses of constant amplitude and varying frequency supplied by the limiter L are impressed upon two vacuum tubes 25 and 25 by way of a coupling condenser 23 and input transformer 24 in such a manner that the tubes are rendered conductive in alternate succession. If the grid of tube 25 is positive, the condenser 2l interposed between the cathodes of the tubes is charged through the tube 25 to the plate battery potential. This charge will then iiow through the tube 26 to the transformer 28 during the following half cycle when the grid of tube 2'6 is at positive potential. This transport of the charges of the condenser 21 will be rel peated in the rhythm of the frequency w3, whereby the current through the transformer 28 will be proportional to the frequency wa at all times. There is segregated from the control magnitude E5 obtained in this manner, by means of a filter F1 a definite component ue whose amplitude varies in proportion to the transmitting period to according to Equation 14 and serves as a direct indication of the distance d. The filter F1 in the example shown is of the bridge type comprising a pair of series resonant circuits 29 and 3|) tuned slightly above and below the frequency of the component u5. All disturbing components of the control potential E5 which fall outside the pass range of this filter are thus suppressed and prevented from impairing the distance measurement. The component us may be measured by means of an alternating current instrument or by a direct current instrument I1 after rectification by means of a rectifier H. This instrument may be directly calibrated in values of distance which is proportional to the rectified or direct potential U5. By impressing a portion of U5 upon the network F2 comprising series condenser 9 and parallel resistance I0, there is produced an additional magnitude Um being proportional tc the differential quotient or rate of change of U5` By measuring this magnitude by means of an additional instrument I2, it is possible to directly indicate the speed or rate of change of the distance d. This indication may be desirable as a navigation aid for aircraft to indicate the rate of ascent or descent, respectively. As is understood, an arrangement as shown in Figure 3 is by no means limited to altitude measurement but may be employed for determining the distance and/or relative speed between any two points or objects.

In the modified arrangement according to Figure 4, high frequency oscillations are produced in the transmitter T2 by the aid of a vacuum tube oscillator Il having anode and grid circuits arranged in regenerative relationship in a manner well known. The tuning capacity 3l is periodically varied in the rhythm of a low frequency o by means of a motor 5l) driving the lshaft of a variable rotary condenser having plates suitably shaped so as to obtain a desired, such as a pure sinusoidal, frequency modulation of the Waves or oscillations eo emitted by the dipole radiator T1 as represented in Equation 34 The dipole is connected to the oscillator in any suitable manner such as by way of coupling coil 32 and a Lecher wire, concentric cable or the like. The receiving antenna R1 is excited by a portion of the radiated oscillations e1 directly and by a further portion e2 after transmission and reliection from the distance point or object (not shown). Due to the difference in travelling time, the two oscillations will cause beats in the receiver R2 having a frequency w3 in such a manner that by virtue of the rectification by tube l5 and amplification in V an intermediate frequency potential e3 is produced according'to Expression 9. The received oscillations are applied to the receiver circuit through a coupling coil 32 and the rectified intermediate frequency signals are transmitted to the amplifier V through a repeater or transformer 38. The tuning of the receiver circuit by means of the variable capacity 3l is synchronized with the tuning variations of the transmitter by directly mounting the variable tuning condenser 3l upon the shaft of the driving motor 56 as indicated in the diagram. In this manner, the receiver tuning corresponds at all times to the momentary transmitting frequency making it possible, even in case of very large frequency swings, to employ a receiver having a comparatively narrow band width thereby ensuring a minimum of interfering signals simultaneously received with the useful signal oscillations.

The intermediate frequency signal es serves on the one hand to produce a potential E3 varying in accordance with the amplitude of the signal e3 by the aid of a rectifying system H3 comprising a double diode rectifier 45, input transformer 46 and smoothing condenser 4l arranged in a manner well understood by those skilled in the art. At the same time the signal e3 is impressed upon a filter or frequency demodulator network Ki comprising in the example shown a pair of series resistances 39 and 39 and a parallel inductance 40, whereby there is developed across the inductance a potential e5 having an amplitude ying in proportion to the frequency of the ut signal es. The signal e is rectied by ins of a double wave rectifier system H1, iprising a pair of diode rectiers il and lll ilting in a control magnitude or potential varying in accordance with the momentary olitude of e3 and in turn being related aciing to a denite law or relationship to the nentary beat frequency w3. If the inductive edance of 4B is small compared with the iic resistance of 39 and 39 the conversion n varying frequency to amplitude will be ac- :ling to the Expression 13. By means of a :r or network F3 which in the example shown iprises a pair of parallel resonant circuits 43 l 43 and a series resonant circuit 12, a dez component u5 is segregated from the poten- E5. This component a5 is amplified by ins of an amplifier Ml forming part of a furr rectifying system H2 and the amplied iponent then rectified by the aid of a double ie rectifier 45, thus obtaining a direct poten- U5 varying in proportion to the amplitude of By comparing U5 and E3 there is obtained ording to the Expression 18 an indication of transmission time substantially independentof any amplitude uctuatons. This comison is effected in the example shown by apng the potentials E3 and U5 to the two dis- :ed coils 48 and 48' of a crossed-co-il ratio ',er I3 indicating the quotient q and in turn transmission period to or the distance d to ietermined. ,rrangements of the type shown in Figure 4 specially suited for use in such cases where signals are subjected to substantial amplie fluctuations during the transmission, such :aused by fading, atmospheric conditions, etc. en using an arrangement as described on a /able craft such as on an aeroplane, ship, etc., steering mechanism of the craft may be di- ;ly controlled by the distance or altitude ;er in such a manner as to maintain a desired iimum height or distance from ground or ob- :les such as mountains or elevated structures, ,o prevent the craft from exceeding a predenined maximum altitude or distance from a in point. This object can be accomplished Ln easy manner by closing a separate electric trol circuit operating the steering mechanism b-y means of electrical contacts cooperating 1 the points or other movable member of the tient meter instrument. ,eferring to Figure 5, there is shown an aliative arrangement for eliminating the effect tmplitude fluctuations of the signals by means a compensation method for indicating the iponent a5 or in turn the distance d to be denined. There is shown an oscillator O comaing an oscillating tube 5l with grid and plate :uits arranged in regenerative coupling reon. The oscillatory or grid tank circuit inies a variable condenser 54 and an iron core uctance coil 53. The frequency modulation zhe oscillations, according to a low frequency s effected by the aid of a toothed wheel 56 becontinuously rotated in front of the iron e of the inductance coil 53 by the aid of a ring motor 55. In this manner the inducte of the coil 53 is varied periodically at a defla frequency 'u resulting in a corresponding luency modulation of the oscillations eo apd to the power amplifier T2 and the transmit- T1. The latter may be a wireless transmitor as shown in the diagram, an electro-acoustic converter or microphone for producing compressional or acoustic waves eo to be transmitted through Water or any other suitable medium. The reflected waves e2 are received by a suitable pick-up device such as a microphone receiver Ri. Disregarding for the moment the arrangements H4 and H5, the oscillations e2 amplied in the receiver R2 are combined or intermodulated with the oscillation et directly transmitted from the transmitter to the receiver by means of a balanced modulating system M comprising a pair of vacuum tubes 58 and 58. The oscillations e2 are applied to the grids of the tubes in opposite phase relation by way of coupling transformer 5l, While the oscillations'eo are applied to the grids in like phase by way of the center tap of the secondary of the transformer 51. By suitable filtering by the aid of condenser 60 there is obtained in the output of the modulator M an intermediate frequency potential e4 having a variable frequency w3. The potential e4 is applied to a network or demodulator K2 comprising series inductances 6| and 6| and parallel resistance 62 and having a propagation ratio dependent upon frequency to produce a potential E5 having an amplitude varying in proportion to the momentary frequency Ws as determined by the lter constants 6|, 6|', 62. The potential E5 is rectified by means of a rectifier Hs comprising four rectifying elements forming a Wheatstone bridge circuit and smoothing condenser 64, and the rectified potential E5 varying in the rhythm of the low frequency determined by the rotation of the disc 56 is passed through a filter F4 comprising series resonant circuit 65 and 65 shunted by a parallel resonant circuit 66 to derive a definite component us in a manner similar to that described hereinabove. This component is impressed upon one coil of a differential relay system P the other coil of which is energized by a portion of the component et through a potentiometer l2 forming part of a balancing system D and having a variable contact member supplying a potential es. By adjusting the potential es by means of the potentiometer 12 in the balancing system D, its amplitude is cornpared with the amplitude of the potential us by the action of the differential relay as described in the following; if the amplitudes of us and ea are unequal, the motor l and with it the geared shaft 'll is set into rotation in the one or the other direction by the differential relay closing the circuit of a positive or negative battery, respectively, energizing the motor. In this manner the potentiometer l2 will be adjusted to a point where the amplitudes of the currents in both relay Windings are equal and the relay armature is maintained in the balance position. 'I'he position of the variable contact member for the potentiometer 'I2 is then an indication of the ampltude ratio between the potentials es and es. This ratio may be directly read on a scale 'I3 calibrated in values of the distance d. In place of an alternating current relay a direct current polarized relay may be employed excited by potentials E5 and Us obtained by rectification of the potentials e5 and ea, respectively.

The frequencies of the oscillations e1 and e2 may be increased before their modulation in M by means of frequency multiplying circuits H4 and H5, thereby obtaining frequencies en and cl2 according to Expression 25 having frequencies wn and w12, respectively, differing by an integer factor n from the original frequencies. Since the frequency of the intermediate signal er obtained as a result of the modulation is increased over the original frequency e3 by the factor n, the indication will now be proportional to nio which may be taken into consideration by a suitable calibration of the indicator. Instead of frequency multiplication, the frequency may be sub-divided to suit existing requirements. In many cases it is desirable to operate a warning signal for extreme values of the distance d. Such a signal which may be of optical o1' acoustic character such as an electric bell '|11 is operated Whenever a predetermined travelling periol to causes a corresponding position of the adjusting member for potentiometer l2 and closes a pair of contacts 713',I

Referring to Figure 6 there is shown an arrangement for selectively measuring a component of the control potential by the aid of a Watt meter type instrument. Item C represents a control circuit comprising an electron tube 83 having its grid connected to the junction point between a series network comprising a condenser 8e and a resistance B5. Such an arrangement results in a watless reaction, whereby the alternating potential on the grid of the tube is displaced by 90 with respect to the plate potential. Accordingly, the plate current is also in quadrature with the plate voltage or in other words, the tube represents a capacitative reactance the value of which depends upon the degree of amplification which may be varied in an easy manner in accordance with the low frequency uo impressed upon the grid by way of choke coil 86. By the aid of this variable electronic capacity .shunted across the oscillatory tank circuit 82 of the regenerative oscillator O, the oscillations generated by the latter are frequency modulated in accordance with the low frequency Variations uo, The oscillations after amplification by means of power amplifier T2 :are converted according to the eX- ample shown in the transmitter T1 into superaudi'ble oscillations or compressional waves en to be transmitted through Water or any other suitab`e medium. A p-ortion er of the oscillations directly reaches the receiver R1 while another p0rtion arrives as a retarded oscillation e2 after travelling to and from a remote object whose distance it is desired to determine. The receiver R1 which may be a microphone or the like serves to translate the mechanical or compressional waves into corresponding electrical oscillations which latter are combined and amplified in the input of tube 9| of the receiver R2 and detected such as by an audion detector 92 provided with a grid condenser 9S and grid leak in a manner well known. The rectified oscillations of intermediate or beat frequency are further amplified by means of an amplifier V, thereby obtaining an alternating potential e3 having a frequency equal to the beat frequency w3. By rectifying a portion of es by means of a circuit Z comprising a rectier 95 and smoothing filter composed of series resistance 9i and a pair of parallel condensers 96 and there is obtained an amplitude control i A. V. C.) potential E3 which is impressed upon the grid of the input amplifier tube 9| in counteracting relation to the amplitude variations of the received signals in such a manner as to maintain the amplitude of the output potential es constant. .As the received oscillations may 'be amplitude modulated in accordance with the low frequency D, the intermediate frequency obtained in the output of the detector 92 may be equally ampitude modulated and in order to suppress this undesired modulation the time constant of the lter S6, 96', 91 is chosen suciently high wi respect to the oscillating period of the low fr quency potential uo. The potential e3 is appli to the filter or demodulator K4 comprising in t1 example shown a series condenser 98 and parallel. resistance 99 to convert the frequen modulated potential into an amplitude modulat potential e5 in substantially the same manner that described in connection with the precedi: figures. The amplitude modulated potential is rectified by the aid of rectiers He consistir in the example shown of a rectifier bridge to o tain a final control potential E5 varying in tI rhythm of the low frequency U.

There is further provided a frequency mr tiplying circuit H7 comprising input transform 8l energized by a portion of the modulating p tential 140 and a pair of rectifiers 88 and 83 a ranged in a double wave rectifying system, wher by an output potential u1 is obtained composed harmonics of the low frequency potential uo. l the aid of a filter F5 comprising parallel coi denser 8% and series inductance 9i) a predete mined component u2 such as the second harmor having a frequency 2v, is segregated from t1 potential u1. The instrument I4 is construct in the fashion of a watt meter and according is responsive only to frequencies which are simu taneously impressed upon the xed coil syste lill energized by potential E5 and the movalt coil |62 energized by potential u2. Since u2 in tI example mentioned contains only the frequen` 2v, only the component us, of E5, which likewi has a frequency 2v, will contribute in produci] an indication, while the inuence of all the oth in part disturbing components is substantial suppressed by this selective indicating methc As a result, the reading of I4 in view of E pressions l and 14 affords an undisturbed indic tion of the path travelled by the oscillations l or in other words, of the distance d to be dete mined. As is understood, the system describl is not limited to acoustic signals but may equally employed for radio and other radiant e: orgy signals in accordance with the spirit of t1 invention. Moreover, details of convention character such as type of tubes, couplings, et may be varied without departing from the spil of the invention.

Referring to Figure 7, there is shown a furth embodiment of the invention designed for mea uring the distance of reflecting points in an ele tric transmission line such as a cable. The c cillation generator O comprises an electron tu |2| provided with regeneratively coupled ano and grid circuits; the grid tank or oscillato circuit comprises a condenser |22 shunted by z inductance coil |23. The grid and plate circu are coupled through a common iron core pr magnetized by a direct current supplied by ba tery |28 upon which is superimposed a low fr quency modulating potential un in such a ma ner as to cause a periodic variation of the ge: erator frequency. The oscillations after amp cation in the power amplifier T2 are impress through a repeater |24 and the primary of further repeater |25 of a decoupling system 'l upon the line or cable Yi-Yz. A short circl at the point X of the line represents a poi from which the oscillations are reflected ba to the transmitting point and applied as retard oscillations e2 through the repeater |25 to t1 modulator Mr. In the latter, which in the exar ple is a balanced modulator, the intermodul tion product between er and e2 is formed in ler similai to that described hereinbefore ing in a beat frequency signal e3 which 'ther amplified by amplier Vi. A portion e signal es serves to produce an A. V. C. tial by means of a system Z1 to maintain ignal amplitude at a constant level in a ier similar to that described in connection Figure 6. The potential e3 is applied to work or demodulating circuit K5 to convert requency modulated potential into a cornding amplitude modulated signal e5 which is rectified by rectifier He, resulting in a control potential E5. The network K5 in sample shown comprises a series resistance parallel inductance, the former being prowith a variable contact member |26 for ting the signal amplitude of E5 which lataries in proportion to the momentary beat ency wa according to a predetermined relaiip determined by the propagation charistics of the network K5. At the same time is produced from the modulating frequency harmonic u1 by the aid of a multiplication n H7 whose frequency may be equal to 2c. harmonic is amplified in V2 and maintained nstant amplitude by the aid of volume con- :ircuit Z2 producing an A. V. C. potential Phe potential u2 of constant amplitude is ed on the one hand to one pair of input nals of the modulator M2 which may be anced modulator as shown in the diagram n the other hand to the other pair of input nals of the modulator M2 in series and `ing relation to the output control potene operation of this arrangement is as folif the component u5 of E5 having a fre- :y equal to 2U has an amplitude equal to mplitude of u2, the frequency 2v in the difce potential (u2-E5) applied to the moduwill disappear and as a result thereof also lirect current component U9 produced in utput of the modulator by intermodulation and (u2-E5). If, on the other hand, us eater or smaller than u2, the input potenapplied to the modulator M2 will include onents of the same frequency 2c in the or opposite phase position in such a manhat a negative or positive direct current onent Us will be included in the modulation ict. This direct current component serves ergize the polarized relay |58 of the con- :ircuit P, thereby starting a motor |60 in )r the other direction. The motor drives idle IGI operating the variable contact |26 the component us of E5 assumes the same .tude as u2. Thus the position of the cons dependent upon the average beat fre- :y w3 and in turn upon the distance travby the oscillations towards and from the ;e point. This distance may be directly read a scale |63 associated with adjustable con- `l26. Since all components of E5 whose fre- :y deviates from 2v will not produce a direct nt of the modulation product and therefore l iot exert any influence on the relay |58, method is highly selective in preventing :irable and interfering components from icing errors and otherwise disturbing the ice indication.

the arrangement according to Figure 8, :ontrol magnitudes are employed for the ice determination. The frequency moduoscillations eo transmitted by the transr T and received as oscillations ez by the Aif) receiver R are mixed or inter-modulated with the non-retarded oscillations ei to produce an alternating potential of varying intermediate frequency w3. After amplification of this potential in amplifier V, two alternating potentials Ee and E7 are produced by transmission through separate slope circuits or networks Kc and K7 to convert frequency changes into amplitude changes, said circuits having different slopes or propagation characteristics dependent on frequency and rectifiers H8 and H9, respectively. The amplitude ratio of a pair of components of like frequency us and uv segregated from the potentials E6 and E7 by means of filters F6 and F7 bears a predetermined relation to the transmitting period to or distance d in accordance with Equation 23. The ratio measurement may be carried out by the aid of an instrument I5 which may be a crossed-coil quotient meter or any other device suitable for indicating the ratio of a pair of signal potentials or currents. Alternatively, the potentials u@ and a7 may be rectified and applied to a direct current quotient meter such as a crossed-coil instrument.

In Figure 9 there is shown a similar arrangement., wherein the comparison of the controlling magnitudes is carried out by the employment of a modulation process. The oscillations e1 directly applied from the transmitter to the receiver R1 are combined with the oscillations e2 received after reflection and rectified in R2, thus producing a potential es at beat frequency w3. By transmission through the networks Ke and K7 and rectiers Ha and H9, potentials Es and E7 are obtained in substantially the same manner to that described in connection with Figure 8. These control potentials vary at loW frequency in proportion to the frequency variation of e3 as determined by the frequency propagation characteristics Ke and K7. In order to effect a selective comparison between two components us and a7 of E4 and E7, respectively, a component u1 of like frequency of us and a7 obtained by the aid of the harmonic producer H7 is applied to the movable system |13 of the watt meter type relay P. The fixed system of the relay comprising the coils |1| and |12 is energized by the components ue and uv in counteracting relation, whereby the torque disappears if these components are equal to each other. Any difference between the amplitudes of the components to be compared causes a corresponding deflection of the relay, thus starting rotation of the servo-motor |14 in the one or the other direction. This motor operates the gear shaft |15 which in turn controls the adjustment of the networks K6 and K7 such as by differentially adjusting a pair of variable potentiometers in a manner similar to that shown in Figure 7 until the amplitudes of the components us and u7 are equalized. This adjustment is dependent upon the average beat frequency w3 due to the frequency propagation characteristics of the networks and accordingly may serve as an indication of the transmitting period to or distance d to be determined. Thus, this system also affords a selective indication due to the fact that all components of E5 and E7 which differ in frequency from u2 will not produce any torque of the relay P.

As will be obvious from the foregoing, there are numerous applications and uses to which the invention may be put. Thus, as pointed out, systems of the type described may serve as an altimeter or terrain clearance indicator to afford a direct reading indication of the height of an aeroplane above ground or the distance from an obstacle in the course of any moving craft. When using acoustic or compressional waves, the invention may serve for depth sounding purposes for use on ships, submarines, etc. Means for producing an automatic warning signal such as shown in Figure may be employed to indicate an extreme or danger condition, or the system according to the invention may serve for automatically controlling a steering device as eX- plained and shown in Figure 4. Furthermore, the invention is not limited to determining the distance of a fixed point but equally applies to the measurement of the distance of movable objects such as aeroplane, ship, etc., from a fixed point on the ground. The invention has a further use in the field of electrical prospecting for investigating geological deposits by transmitting the frequency modulated oscillations in the form of ground waves and receiving oscillations after reflection by geological strata such as mineral or other deposits. Another application resides in the determination of faults or short circuits in transmission lines such as cables as described in connection with Figure 7.

Normally, the transmitter and receiver are arranged at close distance from each other, whereby the direct transmission time to the receiver is of negligibly small value. However, there may be cases such as shown in Figure 10, where it is desirable to place the receiver R at a greater distance d from the transmitter T. In this case the transmitting period of the directly received oscillations e1 will be of appreciable influence in the distance measurement. The transmitting period to measured is determined by the following modiiied expression:

filme C1 C2 wherein c1 represents the speed of propagation over the path to and from the reflecting point and c2 represents the speed of propagation over the direct path from the transmitter to the receiver. The influence of the direct transmission may be rendered small by using different kinds of oscillations whose speed of propagation differs greatly such as electro-magnetic waves for the direct transmission and sound or compressional waves for the transmission to the distant point. In this case the transmission period is determined with suicient approximation by the path b-l-d. In case of equal speed of propagation for the directly and indirectly received oscillations, the transmission time will be as follows:

b-I-d-a c In place of a reflecting point or object, a relay transmitter may be prowded at the remote point arranged to instantaneously retransmit the received oscillation such as indicated diagrammatically in Figure 11. The frequency modulated oscillations of the transmitter T are received by the receiver Rr at the distant point and instantaneously re-transmitted by the transmitter Tr and received by the receiver R with a delay to according to Equation 1. The dierence in transmitting time is determined in the manner described thus enabling a determination or measurement of the distance d between the main transmitter and a distant transmitter located at a remote point. In this manner it is possible. for instance, to determine the distance of an aeroplane from a ground station or the distance between two moving craft such as two planes ii night.

It will be obvious from the foregoing that th invention is not limited to the specic arrange ment of details and steps disclosed and describe: herein for illustration, but that the underlyini idea and principle of the invention are suscepti ble of numerous variations and modification coming within the broad scope and spirit of thl invention as defined in the appended claims The specification and drawings are accordingly tl be regarded in an illustrative rather than a limiting sense.

I claim:

l. A system for measuring the distance between two points in space comprising means located at one of said points for generating oscillatory energy the frequency of which varies according to a predetermined non-linear periodic function with respect to time, means for transmitting a portion of the energy generated to the seconc point and back therefrom to the rst point, mean: for combining the received energy with anothei portion of the energy generated at the rst poim to produce beat energy having a periodically varying frequency depending upon the distance travelled by said rst energy portion to and frorr said second point, further means for converting the beat energy into energy having an amplitude varying according to a predetermined relatior with the beat frequency variations, and means foi segregating and selectively translating the amplitude of a predetermined component of saic last energy.

2. In a system as claimed in claim 1 including means for substantially suppressing amplitude variations of the beat energy prior to its application to said converting means.

3. In a system as claimed in claim 1, said last means comprising iilter means for segregating e predetermined harmonic from the converted energy, and a measuring device calibrated in unit: of distance for indicating the amplitude of saic harmonic component.

4. In a system as claimed in claim 1, said lasi means comprising filter means for segregating a predetermined harmonic from the converted energy, a measuring device calibrated in units oi distance for indicating the amplitude of said harmonic component, and further means to indicate the rate of change of said last amplitude` 5. A system for measuring the distance between two points in space comprising means at one of said points for generating oscillatory energy the frequency of which varies periodically according to a sinusoidal function with respect to time, means for transmitting a portion of the energy generated to the second point and back therefrom to the first point, means for combining the received energy with another portion of the energy generated at the first point to produce beat energy having a periodically varying frequency depending upon the distance travelled by said first energy portion to and from the second point, further means for converting the beat energy into energy having an amplitude varying according to a predetermined relation with the beat frequency variations, and means for segregating and selectively determining the amplitude of a predetermined harmonic coppnent of said last energy.

6. In a system for measuring the distance of a remote object comprising means for `ransmitting a radiant energy signal towards said abject,

frequency of said signal varying according a, predetermined non-linear periodic function h respect to time, means for receiving the sigafter reiiection from said object and for coming the received signal with a local signal of e character to produce a beat signal of varyfrequency depending on the distance travelled the rst signal to and from said object, furr means for converting said beat signal into a ial having an amplitude varying according to yqredetermined relation with the beat frency variations, and means for segregating and actively translating a predetermined harmonic iponent of said last signal.

. In a system for determining the distance of emote object comprising means for transmitg a radiant energy signal towards said object, frequency of said signal varying periodically ording to a sinusoidal function with respect to e, means for receiving the signal after refleci from said object and for combining the refed signal with a local signal of Vlike charer to produce a beat signal of varying frency depending upon the distance travelled by l first signal to and from said object, means substantially suppressing amplitude varia- 1s of said beat signals, further means for conting said beat signal into a signal having an olitude varying according to a predetermined Ltion with the beat frequency variations, and

ins for segregating and selectively indicating amplitude of a predetermined harmonic comrent of said last signal. A system for measuring the distance been two points in space comprising means loed at one of said points for generating oscillay signal energy the frequency of which varies ording to a predetermined non-linear periodic ction with respect to time, means for transting a portion of said energy to the second 1t and back therefrom to the first point, means combining the received energy with another tion of the energy generated at the first point produce beat energy having a periodically ying frequency depending upon the distance felled by said first energy portion to and from 1 second point, means for producing a first tric magnitude proportional to the amplitude aid beat energy, further means for converting l beat energy into energy having an amplie varying according to a predetermined rela- L with the beat frequency variations, means producing a second electric magnitude from l last energy varying in proportion to the gnitude of a predetermined harmonic coment of the converted beat energy, and indicatmeans for determining the ratio between l rst and second magnitudes.

In a system as claimed in claim 8, said last ins being comprised of a quotient indicator rated in units of distance travelled by the energy portion to and from said second it.

l. In a system as claimed in claim 8, said means comprising a device for differentially .bining said electric magnitudes, and amplia adjusting means for at least one of said mitudes having an operating member the p- )n of which indicates the distance travelled he balance condition of said magnitudes, and e means cooperating with said operating uber.

l. In a system as claimed in claim 8, said last lns being comprised of a differential relay energized by said electric magnitudes, a servo-motor arranged to be operated by said relay, amplitude adjusting means for at least one of said magnitudes controlled by said servo-motor, and scale means cooperating with said adjusting means.

12. A system for measuring the distance between two points in space comprising means located at one of said points for generating signal waves, means for non-linearly modulating the frequency of said waves in accordance with a low frequency modulating wave, means for transmitting the modulated waves to said second point and back therefrom to the rst point, means for combining the received wave energy with energy derived directly from said signal waves generated at the rst point to produce beat waves having a periodically varying frequency depending upon the distance travelled by said Waves to and from said second point, means for substantially suppressing amplitude variations of said beat waves, furtherV means for converting said beat Waves into an electric magnitude having an amplitude varying according to the beat frequency variations, means for producing a harmonic component of predetermined order from said modulating wave, further means for deriving a harmonic component of the same order from said magnitude, and means for comparing the amplitudes of said harmonic components.

13. In a system as claimed in claim 12, said last means being comprised of a product forming device responsive only to input currents of like frequency.

14. In a system as claimed in claim 12, said last means being comprised of a watt meter type indicating instrument energized by both said components and calibrated in units of distance travelled by said waves to and from said second point.

15. A system for measuring the distance between two points in space comprising means 1ocated at one point for generating oscillatory signal energy the frequency of which varies according to a predetermined non-linear periodic function with respect to time, means for transmitting a portion of the energy generated to the second point and back therefrom to the first point, means for combining the received energy with another portion of the energy generated at said rst point to produce beat energy having a periodically varying frequency depending upon the distance travelled by said rst energy portion t0 and from said second point, a pair of converting systems having different amplitude propagation characteristics dependent upon frequency energized by portions of the beat energy to produce magnitudes varying in proportion to the beat frequency variations, selective means for segregating harmonic components of a like predetermined order from said magnitudes, and means for comparing the amplitude of said harmonic components.

16. A method of measuring the distance between two points in space comprising the steps of generating oscillatory energy at one of said points, continuously varying the frequency of said energy according to a predetermined nonlinear periodic function with respect to time, transmitting a portion of said energy to the second point and back therefrom to the rst point, combining the received energy with energy generated at the rst point to produce beat energy having a periodically varying frequency depending upon the distance travelled by the rst energy portion to and from said second point, means for converting the beat energy into energy having an amplitude varying according to a predetermined relation with the beat frequency Variations, and segregating and selectively determining the amplitude of a predetermined component of said last energy.

17. A method of measuring the distance between tWo points in space comprising the steps of generating oscillatory signal energy at one point, continuously Varying the frequency of said energy according to a predetermined sinusoidal function, transmitting a portion of said energy to the second point and back therefrom to the iirst point, combining the received energy wi another portion of the energy generated at t1 rst point to produce beat energy having a p riodically varying frequency depending upon tl distance travelled by said first energy portion and from said second point, converting the be energy into energy having an amplitude varyii according to a predetermined relation With t1 beat frequency variations, and segregating ai selectively determining the amplitude of a pr determined harmonic component of the coi verted energy.

GUSTAV GUANELLA. 

